For decades, Lew Hunter's Screenwriting 434 class at UCLA has been the premier
screenwriting course, launching a generation of the industry's most frequently
produced writers. Here, he shares the secrets of his course on the screenwriting
process by actually writing an original script, step by step, that appears in the
book.  from the publisher

If you want to learn about screenwriting, this is the book for you.  Aaron Spelling

I wish this book had been around when I was a student. I heartily recommended it.
For beginners and pros alike.  Steven Bocho

Samuel Goldwyn is reputed to have told a writer: If I want to send a message,
I'll call Western Union. More recent practitioners would advise:
If you want to write a screenplay, read Lew Hunter's Screenwriting 434 
Grant A Tinker

A powerfful and evocative vision into the business and craft of screenwriting.
 Peter Guber

To young, aspiring screenwriters: If it is not possible for you to enroll in Professor
Hunter's class at UCLA, then immerse yourself in his book. It can be the quickest,
surest path to a screenwriting career.  Julius Epstein

An excellent aid to those who want to learn how to write screenplays.  Mike Medavoy